1. Field of the Invention (Technical Field)
The present invention relates to en route spacing of aircraft.
2. Description of the Prior Art
Note that the following discussion refers to a number of publications by author(s) and month and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
En route miles-in-trail (MIT) spacing restrictions are often used to distribute arrival delays upstream of destination airports and to mitigate local areas of en route airspace congestion. National statistics for the U.S. indicate that en route spacing restrictions are applied for approximately 5000 hours per month. These restrictions impact approximately 45,000 flights per month. Current-day practices for MIT-spacing increase controller workload, concentrate traffic unnecessarily, and degrade the performance of conflict-probe (CP) decision support. Today""s procedures also result in inefficient conformance actions that directly impact the airspace user. It is estimated that the fuel penalty alone approaches $45 million per year.
A fundamental goal for en route decision support tool (DST) automation is to assist the controller in providing better Air Traffic Control (ATC) service (i.e., greater flexibility to airspace users and fewer ATC-related deviations to user""s preferred trajectories) while increasing safety and productivity (i.e., reductions or shifts in controller workload that enable additional productivity). The economic benefits to airspace users come in the form of increased capacity/throughput, reduced restrictions and deviations (time and fuel consumption), and increased flexibility to plan and to fly aircraft.
There are many factors that impact air traffic operations, but primary factors include conflicts and Traffic Flow Management (TFM) flow-rate restrictions. Conflicts relate directly to safety while flow-rate restrictions relate directly to the efficient management of capacity-constrained resources (e.g., runways and sectors). Certainly the safety considerations alone warrant the community""s past emphasis on conflict probe technology. However, in terms of mitigating user deviations, particularly in light of the projected rate of traffic growth, it is the flow-rate restriction that is at the core of unlocking user benefits. Although flow restrictions only impact a percentage of flights, the resulting deviations are significant compared to those required for maintaining basic radar separation. Furthermore, the lack of ATC-sector decision support for flow-rate conformance planning and execution results in a significant degradation in the performance of conflict probe. Conflict probe lacks the trajectory xe2x80x9cintentxe2x80x9d of the controller""s plan for flow-rate conformance leading to the xe2x80x9cconflict probingxe2x80x9d of the xe2x80x9cwrongxe2x80x9d trajectories (thus increasing the probe""s rate of false alarms and missed alerts). This degradation occurs in just the sort of xe2x80x9cproblemxe2x80x9d airspace where the air transport industry needs automation assistance such as conflict probe.
It is particularly interesting to consider en route airspace that is subject to dynamic flow-rate restrictions related to local en route bottlenecks (e.g., sector overload) or the transition to/from high-density terminal-areas. NASA has been active in the development and evaluation of tools and techniques for efficient conflict-free planning in the presence of such constraints. The research is based on Center-TRACON Automation System (CTAS) technology. Erzberger, H., et al., xe2x80x9cDesign of Center-TRACON Automation System,xe2x80x9d AGARD Guidance and Control Symposium on Machine Intelligence in Air Traffic Management, Berlin, Germany, May 1993.
In general, two types of flow-rate restrictions must be considered. These include time-based arrival metering and en route miles-in-trail (MIT) spacing. Arrival metering tools for operations within the U.S. and Europe include the CTAS Traffic Management Advisor (TMA), COMPASS, and MAESTRO with future developments including Multi-Center TMA (U.S.) and Arrival Manager (Eurocontrol). Where operational, arrival metering is generally performed in en route airspace within the last 20 minutes of flight prior to entering terminal airspace. Even with arrival metering operations, many flights will still be subject to MIT-spacing restrictions. MIT-spacing procedures can be expected to play a predominant role for several reasons. The first is the ATC-operational need to merge departures with en route traffic that is xe2x80x9cspacedxe2x80x9d for downstream capacity limitations. Second, the limited number of arrival-metering sites (i.e., CTAS-TMA-adapted airports) leaves the remaining airports to depend on MIT-spacing procedures. Third, there is a need to occasionally propagate delays upstream of terminal airspace prior to the arrival-metering horizon. As traffic growth outpaces capacity, more flights will be affected by dynamic flow-rate initiatives including MIT-spacing restrictions.
Much of the en route decision support tool effort within the U.S. and Europe has focused on near-term implementations of conflict probe and arrival metering capabilities. There has been some long-term progress towards the development of advanced advisory tools that integrate capabilities for conflict detection/resolution and flow-rate conformance for arrival metering. Green, S. M., et al., xe2x80x9cField Evaluation of Descent Advisor Trajectory Prediction Accuracy for En route Clearance Advisories,xe2x80x9d AIAA-98-4479, AIAA Guidance, Navigation, and Control Conference, Boston, Mass., August 1998; Slattery, R. et al., xe2x80x9cConflict-Free Trajectory Planning for Air Traffic Control Automation,xe2x80x9d NASA TM-1 08790, January 1994; Green, S. M., et al., xe2x80x9cEn route Descent Advisor (EDA) Concept,xe2x80x9d Advanced Air Transportation Technologies Project Milestone 5.10 Report, September 1999, M/S 262-4, NASA Ames Research Center, Moffett Field, Calif.; and Swenson, et al., xe2x80x9cDesign and Operational Evaluation of the Traffic Management Advisor at the Fort Worth Air Route Traffic Control Center,xe2x80x9d 1st USA/Europe Air Traffic Management RandD Seminar, Saclay, France, June 1997. The Descent Advisor tool of Green et al. (now referred to as the En route/Descent Advisor (EDA)) has undergone many refinements to its controller interface, trajectory planning, and conflict-probe capability to support near-term operational implementation of simple spin-off capabilities. McNally, B. D., et al., xe2x80x9cController Tools for Transition Airspace,xe2x80x9d AIAA-99-4298, AIAA Guidance, Navigation, and Control Conference, Portland, Oreg., August 1999; Erzberger, H., et al., xe2x80x9cConflict Detection and Resolution In the Presence of Prediction Error,xe2x80x9d 1st USA /Europe Air Traffic Management RandD Seminar, Saclay, France, June 1997; and Laudeman, I. V., et al., xe2x80x9cAn Evaluation and Redesign of the Conflict Prediction and Trial Planning Graphical User Interface,xe2x80x9d NASA TM-112227, April 1998. However, there has been little effort on near-term controller tools to assist with flow-rate conformance, let alone integration with conflict detection/resolution. Furthermore, there has been no emphasis on the en route spacing problem.
In the U.S., traffic management coordinators (TMCs) within each ATC facility are responsible for coordinating MIT-spacing initiatives within their facility when needed. Dynamic initiatives are either generated within the facility (e.g., local arrival spacing to a non-metered airport), received from neighboring facilities, or coordinated through the ATC System Command Center (ATCSCC). MIT-spacing restrictions are defined in terms of a stream of flights, spacing-reference fix, active period, and a spacing requirement (e.g., 20 nm in trail). Restrictions may also segregate streams by altitude stratum and/or arrival routing.
Once an MIT-spacing restriction is initiated, local TMCs identify the flights within their facility that are affected by the restriction. TMCs then coordinate re-routes to form xe2x80x9cfreeways in the skyxe2x80x9d that allow sector controllers to visualize the stream and determine the maneuvers necessary for conformance. Controllers primarily use vectors to establish and maintain the desired spacing. The xe2x80x9cpath-dependentxe2x80x9d nature of this process makes MIT-spacing restrictions operationally feasible to implement, monitor, and control across sector boundaries, with little or no automation assistance.
TMCs assess each MIT-spacing situation and determine the appropriate sectors, upstream of the spacing-reference fix, to begin coordinating controller actions for conformance. This effective range (or time horizon) for controller conformance depends on the available airspace and the magnitude of delays. Traffic streams nominally have a natural spacing: the greater the difference between the nominal and required spacing, the greater the delay resulting from conformance. Depending on the magnitude of the delays and available airspace, it may be necessary to propagate MIT-spacing restrictions to upstream facilities via xe2x80x9cpass-backxe2x80x9d restrictions (with coordination facilitated by the ATCSCC).
FIG. 1 illustrates an example scenario for Chicago""s O""Hare Airport where it is not uncommon for delays to propagate upwards of 1000 nm upstream. The xe2x80x9cdelayabilityxe2x80x9d of a flight (i.e., the operationally acceptable amount of delay that can be absorbed) grows with the range-to-go and airspace capacity. As terminal-area delays grow, Chicago Center must throttle the arrival flow. Even with airborne holding, the back up of arrival traffic can saturate the airspace. Chicago Center then coordinates a restriction with Minneapolis Center to space incoming arrivals (e.g., 10 MIT by Fort Dodge (FOD)). Depending on the situation, Minneapolis may in turn need to slow the rate of incoming traffic from Denver Center (e.g., 20 MIT by Oneil (ONL)).
Even if high-density terminal areas (such as Chicago) convert to time-based arrival metering, MIT-spacing initiatives still provide TMCs with an effective means for dynamically distributing excess delay upstream. MIT initiatives have a significant operational advantage in that they are relatively straightforward to delegate (within and between ATC facilities), implement, and monitor. When flights are formed into in-trail streams, controllers are able to visualize and control spacing at the sector without automation assistance.
The frequency, source, and impact of MIT initiatives vary widely from day to day as dynamic changes in traffic load exceed airspace capacity (primarily due to weather). National statistics for 1998, xe2x80x9cQuarterly Restriction Report, Third Quarter 1998,xe2x80x9d Federal Aviation Administration David J. Hurley Air Traffic Control System Command Center (ATO-200), Reston, Va., indicate that the number of restriction hours averaged approximately 5000 hours per month (plus or minus 15%).
A detailed study of Denver Center operations was conducted to estimate the number of flights impacted by MIT restrictions within that facility. The objective was to estimate the frequency with which MIT-spacing restrictions were imposed and the number of flights affected. The study focused primarily on traffic to the top four destination airports that resulted in restrictions on Denver Center: Los Angeles (LAX), Chicago (ORD), Dallas/Ft. Worth (DFW), and Las Vegas (LAS). Data was collected for June 1996. These data included the Traffic Management Unit (TMU) logs (noting the duration and nature of MIT restrictions), and recordings of the hourly sector traffic count as a function of destination.
FIG. 2 presents the results from the study in terms of a three-dimensional pie chart to illustrate the average daily volume of impacted flights. The cross section of each column indicates the percentage of days for which MIT initiatives were active. The radius indicates the average number of flights per hour affected by restrictions for that airport. The column height represents the average duration of initiatives on an active day. Some active days involve multiple initiatives (e.g., Chicago may call for restrictions for 60 min in the morning and 90 minutes in the afternoon).
On a weekly basis, the figure indicates that 163 flights within Denver Center are affected by MIT-spacing restrictions for the top four destination airports. The number of flights per hour affected by restrictions averaged 10 for LAX, 10 for ORD, 9 for LAS, and 8 for DFW. The combined data for the four destinations indicate that approximately 9 flights per restriction hour were affected by spacing initiatives. Although restrictions tend to be relatively heavy for the month of June (due to thunderstorm impact on sector capacity), these results were relatively light and considered to be representative of the annual average for Denver.
An additional study, Klopfenstein, M., et al., xe2x80x9cEn route User Deviation Assessment,xe2x80x9d RTO-37 Final Report, Contract # NAS2-98005, NASA AATT Project Office, NASA Ames Research Center, Moffett Field, California, November 1999, performed a nation-wide analysis of the frequency of, number of flights impacted by, and reasons for MIT restrictions. The data set included ATCSCC logs of imposed MIT restrictions as well as flight plan and track data archived from the En route Traffic Management System (ETMS). The study analyzed 54 days of traffic, sampled between November 1998 and October 1999, representing the gamut of operations (peak holiday traffic, severe weather, and routine operations). The number of restrictions implemented per day ranged from 69 to 346 with an average of 186. These restrictions impacted an average of 13.5 aircraft per restriction with an average rate of 8.5 flights per restriction hour.
Table 1 presents the top four categories of restrictions noted in the traffic management logs. These account for 85% of the restrictions studied. Approximately two thirds of the restrictions were attributed to traffic volume and weather. Whereas the weather category captures situations involving reduce airspace capacity due to weather, the volume category captures situations involving excess volume. The next largest categories, traffic demand and reduced airport acceptance rate (AAR) contributed to 21% of all restrictions. The AAR category captures situations involving delays due to a reduction in airport capacity. A clear definition of the demand category was never found. In total, these top four categories impacted approximately 2.4% of all flights within the national airspace system (NAS).
Table 2 categorizes the same data set by destination. Traffic streams are often defined by destination even though many restrictions are not directly related to the destination itself. This enables traffic managers to quickly identify flight groups that, if restricted, will solve the problem with one restriction. This xe2x80x9cleast common denominatorxe2x80x9d also simplifies the communication of the restriction to other traffic managers and individual sectors. Although this technique may not result in an equitable distribution of delay, it is a practical approach that has evolved from operational necessity.
Chicago and Atlanta arrivals account for nearly one fourth of all MIT restricted flights. This is not surprising given their status as two of the busiest hub airports: airport delays impact a large number of flight arrivals; and for en route delays, changes to their arrival streams can effect a significant change to the traffic environment.
Although today""s xe2x80x9cmanualxe2x80x9d MIT-spacing techniques are straightforward to implement, there are several disadvantages related to their path-dependent nature. From the airspace-user""s point of view, deviations from their preferred trajectory come in three forms:
TMC-initiated re-routes to establish a stream;
controller vectors to establish spacing; and
controller vectors for conflict resolution.
FIGS. 3 and 4 illustrate the problem. Three flights are initially on user-preferred eastbound routes. The circles indicate the relative sequence of the un-delayed flights when the first flight crosses the boundary. The natural order of arrival at the boundary is B, C, and A. Consider the situation where the downstream center (ARTCC 2) imposes an MIT-spacing restriction at the boundary. Without automation assistance, it would be difficult for sector controllers to visualize and space their flights relative to flights in other sectors that are orthogonal to the flow. Referring to FIG. 3, the controller in sector 2 would have difficulty in spacing B relative to A or C. To overcome this problem, TMCs coordinate the re-routing of A and C (FIG. 4) to form a stream that can be visualized and controlled by sectors 2 and 5. Depending on the natural distribution of flight paths, these re-route actions add a significant penalty.
Once streams are formed, spacing adjustments typically involve vectors. Although speed control can help fine-tune spacing under current procedures, it is often too little to establish spacing because of performance mismatches and limited range within a sector (for speed changes to take effect). In-trail flows also reduce the opportunity for faster aircraft to pass slower. ones when the faster aircraft would naturally arrive first at the spacing-reference fix. Once spacing is established within a stream, additional deviations may result from conflicts with crossing traffic.
From the ATM point of view, current-day spacing procedures present several disadvantages. First is the workload required to establish the stream. Second, controllers must rely on tactical techniques to establish spacing based on experience and trial and error. Third, in-trail techniques force flights into streams that concentrate traffic density and workload in the xe2x80x9cspacingxe2x80x9d sectors as opposed to distributing flights across sectors. Finally, the spacing sectors are impacted in terms of conflict detection and resolution because the tactical nature of current-day spacing techniques negatively impacts the operational use of CP tools.
Regarding conflict detection, consider the situation illustrated in FIG. 5. The two eastbound flights are subject to a spacing restriction while the other two flights represent crossing traffic. The solid lines indicate the path used by CP. The spacing-conformance path for the first eastbound flight is also shown in a dashed line. CP has no knowledge of the controller""s plan for spacing conformance until the conformance maneuvers are completed. More often than not, such plans are not updated or reflected in the ATC Host computer. This is due to several factors including the controller workload associated with flight plan amendments and the difficulty controllers would have in reflecting today""s relatively tactical spacing techniques in a flight-plan amendment. As a result, CP may experience a greater rate of false alarms (due to the lack of spacing-conformance intent) and missed alerts (if the controller""s conformance actions result in a new conflict).
With the present invention, in the near term, there are many opportunities to enhance current and emerging technologies such as those being deployed in the U.S. under the FAA""s Free Flight Phase 1 (FFP1) program. For the purposes of the specification and claims, Conflict Probe (CP) refers to a basic en route conflict-probe capability. CP assists the controller by predicting problems based on flight plans and radar-track data (e.g., loss of minimum-required separation between two flights) and providing trial-planning support to formulate and coordinate resolution actions.
Two near-term enhancements to CP technology provided by the present invention can go far in reducing user deviations from their preferred trajectories. First, a tool is provided to help en route controllers efficiently conform to flow-rate restrictions. This will enable controllers to strategically plan conformance actions resulting in reduced workload, flight deviations and fuel consumption. The second enhancement to CP involves the integration of conflict detection and resolution capability with flow-rate conformance. Integration will further reduce fuel consumption and workload by reducing the conflict-probe false-alarm and missed-alert rates. This improved accuracy, due to better knowledge of the controller""s intended conformance actions, will reduce the number of corrective clearances needed to achieve flow-rate conformance while avoiding conflicts. As a first operational step, there should be a large return on investment in applying CP technology (conflict detection and trial planning) to flow-rate conformance. Although the manual trial-planning approach is too cumbersome for arrival metering (which involves complex trajectory-planning challenges with high densities due to traffic compression and merging near the terminal area), CP technology lends itself well to en route spacing operations, as demonstrated by the present invention.
Another enhancement provided by the present invention is the addition of automatic xe2x80x9cmeet-spacingxe2x80x9d advisory capabilities to reduce controller work in manually trial planning spacing conformance solutions. The invention provides for automated advisories (a la EDA milestone 5.10 techniques) to advise combined speed, altitude, and/or path-stretch vectors to achieve spacing conformance. The EDA techniques described in Erzberger, H., et al., xe2x80x9cDesign of an Automated System for Management of Arrival Trafficxe2x80x9d, NASA TM-102201, June 1989, focused on arrival spacing only (not en route and departure), along fixed arrival routes only (not flexible paths), and only offered limited descent-speed advisories. Other references relating to the EDA techniques are Green, S., et al., xe2x80x9cField Evaluation of Descent Advisor Trajectory Prediction Accuracy for En route Clearance Advisories,xe2x80x9d AIAA-98-4479, AIAA Guidance, Navigation, and Control Conference, Boston, Mass., August 1998; Slattery, R. et al., xe2x80x9cConflict-Free Trajectory Planning for Air Traffic Control Automation,xe2x80x9d NASA TM-108790, January 1994; and Green, S. M., et al., xe2x80x9cEn route Descent Advisor (EDA) Concept,xe2x80x9d Advanced Air Transportation Technologies Project Milestone 5.10 Report, M/S 262-4, NASA Ames Research Center, Moffett Field, California.
The present invention is of a method of, and a system and software for, minimizing aircraft deviations needed to comply with an en route miles-in-trail spacing requirement imposed during air traffic control operations, comprising: establishing a spacing reference geometry; predicting spatial locations of a plurality of aircraft at a predicted time of intersection of a path of a first of said plurality of aircraft with the spacing reference geometry; and determining spacing of each of the plurality of aircraft based on the predicted spatial locations. In the preferred embodiment, the spacing reference geometry can be any of fixed waypoints, including navaids, airway intersections, and predetermined latitude/longitude positions, airspace sector boundaries, arcs defined in reference to an airport or other geographical location, spatial lines, and combinations of spatial line segments. Both predicted spatial locations and determined spacing of each aircraft are displayed, with the determined spacing preferably in an alphanumeric format on a predetermined location on a display in list form, on the flight data tags of a primary traffic (xe2x80x9cRxe2x80x9d-side) display, on the primary traffic (xe2x80x9cRxe2x80x9d-side) display on or near the aircraft target, on flight-progress strips, and/or on URET CCLD displays. A proposed alteration in flight characteristics (course, speed, altitude, and combinations thereof) of one or more of the aircraft may be set, after which locations and spacings are recalculated based upon the proposed alteration, thereby providing feedback as to conformance of the proposed alteration with the spacing requirement, and preferably together with employing a conflict probe to predict aircraft conflicts in view of the proposed alteration. The controller may specify whether the spacing determination employs spacing calculation parameters including rolling spacing, fixed spacing, absolute spacing-distance, and relative spacing distance parameters. A meet-spacing requirement may be imposed, whereby changes to course, speed, and altitude for one or more of the plurality of aircraft are automatically proposed to a controller that would meet the spacing requirement. The aircraft may be selected by a matching aircraft to input stream characteristics, as well as by directly identifying flights by controller input, and the selection may be reperformed at repeated intervals. Spacing advisory data is preferably reported to other controllers responsible for monitoring each aircraft. The software of the invention is preferably a modular component of a Center-TRACON Automation System. The invention is additionally of computer media comprising the computer software of the invention.
The invention is further of a computer system comprising one or more central processing units, one or more displays, one or more input devices, an en route miles-in-trail planning software component, and a conflict probe component.
A primary object of the present invention is to provide to en route controller a system and method to efficiently conform to miles-in-trail (MIT) spacing restrictions.
An additional object of the present invention is to provide such controllers with a system and method that also is integrated with conflict probing to reduce its false-alarm and missed-alert rates.
A primary advantage of the present invention is that it reduces workload and fuel consumption by reducing the number of corrective clearances (needed to achieve flow-rate conformance while avoiding conflicts) and the more efficient distribution of spacing workload upstream and across sectors.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.